str_startswith: New module.

* lib/string.in.h (str_startswith): New declaration.
* lib/str_startswith.c: New file.
* m4/string_h.m4 (gl_STRING_H_REQUIRE_DEFAULTS): Initialize
GNULIB_STR_STARTSWITH.
* modules/string-h (Makefile.am): Substitute GNULIB_STR_STARTSWITH.
* modules/str_startswith: New file.

ChangeLog

@@ -1,3 +1,13 @@
+2025-01-03  Bruno Haible  <bruno@clisp.org>
+
+	str_startswith: New module.
+	* lib/string.in.h (str_startswith): New declaration.
+	* lib/str_startswith.c: New file.
+	* m4/string_h.m4 (gl_STRING_H_REQUIRE_DEFAULTS): Initialize
+	GNULIB_STR_STARTSWITH.
+	* modules/string-h (Makefile.am): Substitute GNULIB_STR_STARTSWITH.
+	* modules/str_startswith: New file.
+
 2025-01-02  Bruno Haible  <bruno@clisp.org>
 
 	gnulib-l10n: Clarify the license of the POT file.

lib/str_startswith.c

@@ -0,0 +1,29 @@
+/* str_startswith function.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation, either version 3 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2025.  */
+
+#include "config.h"
+
+/* Specification.  */
+#include <string.h>
+
+
+int
+str_startswith (const char *string, const char *prefix)
+{
+  return strncmp (string, prefix, strlen (prefix)) == 0;
+}

lib/string.in.h

@@ -1077,6 +1077,14 @@ _GL_WARN_ON_USE (strtok_r, "strtok_r is unportable - "
 /* The following functions are not specified by POSIX.  They are gnulib
    extensions.  */
 
+#if @GNULIB_STR_STARTSWITH@
+/* Returns true if STRING starts with PREFIX.
+   Returns false otherwise.  */
+_GL_EXTERN_C int str_startswith (const char *string, const char *prefix)
+     _GL_ATTRIBUTE_PURE
+     _GL_ARG_NONNULL ((1, 2));
+#endif
+
 #if @GNULIB_MBSLEN@
 /* Return the number of multibyte characters in the character string STRING.
    This considers multibyte characters, unlike strlen, which counts bytes.  */

m4/string_h.m4

@@ -1,5 +1,5 @@
 # string_h.m4
-# serial 39
+# serial 40
 dnl Copyright (C) 2007-2025 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -70,6 +70,7 @@ AC_DEFUN([gl_STRING_H_REQUIRE_DEFAULTS],
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STRSTR])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STRCASESTR])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STRTOK_R])
+    gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_STR_STARTSWITH])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_MBSLEN])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_MBSNLEN])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_MBSCHR])

modules/str_startswith

@@ -0,0 +1,23 @@
+Description:
+str_startswith() function: test whether a string starts with a given prefix.
+
+Files:
+lib/str_startswith.c
+
+Depends-on:
+string-h
+
+configure.ac:
+gl_STRING_MODULE_INDICATOR([str_startswith])
+
+Makefile.am:
+lib_SOURCES += str_startswith.c
+
+Include:
+<string.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+all

modules/string-h

@@ -69,6 +69,7 @@ string.h: string.in.h $(top_builddir)/config.status $(CXXDEFS_H) $(ARG_NONNULL_H
 	      -e 's/@''GNULIB_STRSTR''@/$(GNULIB_STRSTR)/g' \
 	      -e 's/@''GNULIB_STRCASESTR''@/$(GNULIB_STRCASESTR)/g' \
 	      -e 's/@''GNULIB_STRTOK_R''@/$(GNULIB_STRTOK_R)/g' \
+	      -e 's/@''GNULIB_STR_STARTSWITH''@/$(GNULIB_STR_STARTSWITH)/g' \
 	      -e 's/@''GNULIB_STRERROR''@/$(GNULIB_STRERROR)/g' \
 	      -e 's/@''GNULIB_STRERROR_R''@/$(GNULIB_STRERROR_R)/g' \
 	      -e 's/@''GNULIB_STRERRORNAME_NP''@/$(GNULIB_STRERRORNAME_NP)/g' \